Think in todays terms if a mob began firing rockets into a U.S. Army or U.S. Navy base in any state in the Union. What would the immediate reacting be from Washington?
The Civil War began with South Carolina's pro-slavers triggering domestic rebellion. Whatever methods were necessary in order to fully crush the hot bed of sedition were required in forcing the enemy into surrendering.
???? The 1861 bombardment of Fort Sumter came from the various forts and artillery at Fort Moultrie, Morris Island, Point Johnson, Sullivan's Island, Cummons Point, etc., not from cannon in the city (if there were any in the city at that time). Crowds of spectators lined the Battery in Charleston watching the distant battle.
Two big cannon having an effective range of five miles were placed on the Battery in 1863, but the first one blew up on the first shot. I don't know how effective those cannon ever were. Fort Sumter was in Confederate hands then anyway. There had been cannon on the Battery for the War of 1812, but a modern painting I've seen shows no guns on the Battery in 1860.
I took a walking tour of Charleston last fall. The guide showed us pictures of houses that were standing then that are still standing now. We did walk the Battery in that tour. The carriage tours were better though. More humor and easier on the feet.
I'll let your 'extremist' remark pass because you don't know any better.